Identify groups of continuous numbers in a list

Question

I\'d like to identify groups of continuous numbers in a list, so that:

myfunc([2, 3, 4, 5, 12, 13, 14, 15, 16, 17, 20])

Returns:

Answer 1

The versions by Mark Byers, Andrea Ambu, SilentGhost, Nadia Alramli, and truppo are simple and fast. The 'truppo' version encouraged me to write a version that retains the same nimble behavior while handling step sizes other than 1 (and lists as singletons elements that don't extend more than 1 step with a given step size). It is given here.

>>> list(ranges([1,2,3,4,3,2,1,3,5,7,11,1,2,3]))
[(1, 4, 1), (3, 1, -1), (3, 7, 2), 11, (1, 3, 1)]